(1) Field of the Invention
The present invention relates to a temperature compensating voltage generator circuit, and more particularly to a temperature compensating voltage generator circuit used for temperature compensation of electric circuits whose electric characteristics can be controlled by a control voltage.
(2) Description of the Prior Art
In general, an electric characteristic of an electric circuit such as a gain or an oscillation frequency of an amplifier or an oscillator changes due to the change of the temperature of the surroundings and, therefore, such an electric circuit comprises a means for temperature compensation. For example, as illustrated in FIG. 1, a control voltage such as a DC bias potential of an electric circuit CKT, such as an amplifier which is operated by an operating voltage V.sub.CC, is produced by a control voltage generator circuit, i.e., temperature compensating voltage generator circuit consisting of resistors R1 and R2 and a negative coefficient temperature sensitive resistor S, and, the control voltage is changed in accordance with the change of the ambient temperature, so that the electric characteristic such as the gain of the electric circuit CKT is maintained in a constant condition.
Since the theoretical estimation of the temperature characteristics of the electric circuit CKT is generally difficult, the temperature characteristics are practically measured by using the practical circuit device and the resistors R1 and R2 and the negative temperature coefficient temperature sensitive resistor S are selected. However, in many cases the temperature characteristics of the electrical circuit CKT do not show simple or linear curves, so that conventional means cannot effect substantially complete temperature compensation and it takes a long time to determine the characteristic of the temperature compensating voltage generator circuit. When the characteristics of the electrical circuit CKT have changed due to the variation over a period of time, it is necessary to stop the operation of the electric circuit CKT in order to readjust the characteristics of the temperature compensating voltage generator circuit.
When it is necessary to effect complete temperature compensation, the characteristic of the electric circuit is practically measured at various temperatures and the control voltages, i.e., the temperature compensating voltages at the measured temperatures are determined so that the characteristic of the electric circuit is equalized. However, in the conventional temperature compensating voltage generator, it is impossible to adjust the value of the control voltage independently at various temperatures, so that the adjustment of the compensating voltage of the temperature compensating voltage generator circuit is very difficult. For example, when the compensating voltage is adjusted at another temperature after an adjustment of the compensating voltage at a base temperature, for example a normal temperature, the compensating voltage at the base temperature which is previously adjusted, changes.
Moreover, in the above-mentioned conventional circuit, when the temperature characteristic of the control voltage for effecting temperature compensation cannot be approximated by a first order curve, it is very difficult to effect temperature compensation.